Following the success of electric keyboards and guitars, innovators have created the electronic counterparts of other acoustic instruments, including drums.
In providing the electronic counterpart of acoustical drums, small circular resilient pads are often used to convert the strike of the player's drumsticks into electronic impulses that are in turn converted into synthesized, drumlike sounds. These electronic drum pads represent one kind of electronic percussion instrument for creating the synthesized drum sounds. Drum pads are typically made with stretched skin backed by a light density foam material over a transducer soundboard. An example of the electronic drum pad is found in U.S. Pat. No. 4,947,725. While electronic pads of this kind have enjoyed a following among musicians and audio engineers, the pads have not been able to provide the same feel and texture as the drum heads of the acoustic snare, tom and bass.
While electronic percussion instruments have the advantage of controlled output and the ability to produce a wide variety of sounds, they do not play the same as an acoustic drum. There is a definite disadvantage to the drummer in that the look, feel, and response of most electronic drums fail to give the player anything remotely similar to the response rhythm that a traditional acoustic drum provides. Since drummers acquire their technical ability from acoustic drums, the changeover to electronic pads may be unacceptable to some performers and less than optimum for others. The disadvantages are primarily in the feel of the sticks as they strike the simulated drum surface and in the drummer's motor memory in reaching for the usual placement and strike area of conventional acoustic sets.
In order to try and solve the problems associated with the feel of electric drums innovators have tried to use acoustic drums in place of the electronic pads as the triggering mechanism for a drum synthesizer. Generally, these devices use a transducer mounted on the acoustic drum in order to detect the impact of the drumstick on the drum head. There are three basic methods for mounting transducers on acoustic drums: air coupling including internal mounting, head mounting, and shell mounting.
Air coupling uses a transducer, typically a microphone, placed in close proximity to the drum head to detect air movement produced by the vibrating drum head. Because the transducer cannot readily discriminate the source of the air vibration, external air coupling is highly susceptible to background noise and produces a high percentage of false triggers. While internal mounting of the microphone within the internal cavity of the drum shell reduces the instances of false triggers it requires extensive modification to the drum and significantly alters the acoustic properties of the drum. Even in drums which use internal mounting for air coupling, there is a high incidence of false triggering. Another disadvantage to air coupling is that attached transducers tend to be mechanically unreliable and typically require a separate power source.
Head mounting uses a transducer, typically a piezoelectric element, glued or taped to the drum head to directly detect the vibration of the drum head. This method of mounting a transducer also suffers from a high incidence of false triggering because of the long duration for which the drum head continues to vibrate after it is initially struck. An acoustic drum head will vibrate much longer after it is struck than the pads typically used in electronic drums. Another disadvantage is that the acoustics of the drum are corrupted by mounting a transducer on the drum head. Additionally, head mounted transducers are inherently unreliable because the adhesives used are often unable to withstand the constant vibration of the drum head and eventually fall off.
Shell surface mounting uses a transducer, typically a piezoelectric element, screwed or glued to the inside or outside wall surface of the drum shell. While mechanically more reliable than air coupling or head mounting, shell surface mounting still suffers from an inability of the transducer sensor to discriminate between individual drumstick strikes on the drum head and background noise. Depending upon how and where the transducer is mounted, this method may also result in a degradation of the acoustic properties of the drum.
All three of these mounting methods share the disadvantages of being susceptible to false triggering, varying degrees of mechanical unreliability, and possible corruption of the acoustic characteristics of the drum. The most significant of these shortcomings is the problem of false triggering from background noise or retriggering caused by the long duration of the drum head vibration caused by a drumstick strike. This problem is typically overcome by setting the sensitivity threshold level where only the hardest strikes are registered by the drum synthesizer. While this may reduce the number of false triggers and retriggers, it severely limits the range of drumstick strikes which the synthesizer will register. This in turn will require the drummer to increase the force with which they strike the head in order to guarantee the strike registering.
Alternatively the drum may be dampened in order to increase the range of strikes the synthesizer will register, but this method effectively eliminates the acoustic functionality of the drum. An example of a dampened drum with an electronic sensor is found in U.S. Pat. No. 5,293,000.